Field of the Invention
The present invention relates to a gear unit for an actuating drive, in particular a window lifter drive, of a motor vehicle, comprising a gear housing and comprising a pivot bolt which is rotatably fixedly connected thereto to rotatably support a gear wheel, in particular of a worm gear.
Description of the Background Art
A window lifter, in particular a so-called cable window lifter, as the actuating drive of a motor vehicle, usually has an electric motor and a gear in the form of a worm gear, whose worm wheel, which is rotatably supported in the gear housing, has a helical gearing on the circumferential side and which engages with a worm which is disposed on the free shaft end of the motor shaft and fixed to the shaft. The rotation axis of the worm gear of the 90° deflection gear formed thereby is typically formed by a pivot bolt which is rotatably fixedly seated in the gear housing. In the case of the cable window lifter, the worm wheel is usually coupled with a cable drum oriented coaxially to the rotation axis of the worm wheel. The window lifter cable, which, in turn, is connected to the particular vehicle window pane via drivers, is wound several times around the cable drum in order to lift or lower the window pane, depending on the direction of rotation of the actuating drive formed by the electric motor and the gear.
The pivot bolt, onto which the worm wheel and possibly the cable drum are rotatably supported, is typically a steel pin or bolt having ribbing, which is referred to as knurls, on its one end, by means of which the bolt is rotatably fixedly seated on the base of the gear housing. For this purpose, this knurled or ribbed area of the bolt is usually injection-molded with plastic during plastic injection molding of the gear housing.
The manufacture of a pivot bolt of this type is complex and cost-intensive to the extent that, to achieve its required surface condition, the steel pin provided for this purpose as the base body must usually be ground in at least two stages regardless of whether the knurling is introduced into the steel pin before or after the grinding process. The reason for this is that the region or section of the steel pin into which the knurling is introduced, usually has a larger outer diameter than the outer diameter of the pivot section of the steel pin or bolt, which is properly used as the bearing surface for the worm wheel. Accordingly, the steel pin or bolt may not be easily subjected to through-feed grinding. Instead, its bearing surface and knurled section must be ground individually in a cost-intensive special grinding process, for example infeed grinding. Since the surface of the steel bolt is damaged during knurling, a further grinding process is necessary subsequent to the knurling of the corresponding pivot section of the steel bolt in order to achieve the required surface condition.